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4 From: wagons@connriver.net (Daniel Wing)
5 Subject: Long Technical Post 1
7 Message-ID: <wagons-0301041020310001@port-1-26.wellsriver.connriver.net>
8 Organization: Cookeville Garage
9 Newsgroups: rec.food.sourdough
12 Some members of this newsgroup will remember that I have posted some of
13 the content of my correspondence with Michael Ganzle, a German sourdough
14 researcher. He has recently reviewed a proof of a book I have written
15 about masonry ovens and naturally fermented bread, and has commented in
16 detail. Those comments will interest those of you who are interested in
17 the science and technology of sourdoughs. This post and others that follow
18 are for you. If you ARE NOT linterested in the subject, stop here, and
19 save yourself from confusion and frustration.
20 In each section Michael quotes a sentance from the book, and then responds:
21 ------------------------------------
22 "witness the profusion of instant yeast brands-- while the opposite is true³
24 I strongly appreciate the notion that the "time equals money equation³ is
25 not true for sourdough bread or any kind of other fermented foods-- wine,
26 soy sauce, cheese, vinegar, fermented sausage: they usually get better if
27 they are fermented for a long time (the definition of "long³ varies,
28 though, with the different foods).
29 -------------------------------------
30 "I triple it by mixing it with its weight of water and its weight of flour³
32 There is a microbiological explanation for the three stage sourdough
33 processes. Microbial growth can be divided in three stages. When the
34 organisms are transferred to a new environment (e.g. by refreshing a
35 sourdough that has been in the refrigerator), they take some time to
36 adapt; no growth occurs ("lag phase³). Once the organisms are familiar
37 with the new environment, they start to grow exponentially, meaning one
38 doubling of cell counts in a given time (generation time), so called "log
39 phase³. Eventually, the culture will become stationary, i.e. the organism
40 have run out of food, or are inhibited by the metabolic end products. For
41 effective sourdough fermentation, one needs a lot of metabolically active
42 cells. After three or more refreshments, the organisms will reliably start
43 to grow soon after inoculation and will produce enough carbon dioxide.
44 Things are different with yeast dough, though: there simply are so many
45 cells that these have to cough only once to raise the dough.
46 --------------------------------------------
47 "the time it was inoculated and to the temperature at which it is kept
48 than with the size of the inoculation.] Let's call this the second leaven³
50 Comment No1: Weıve been doing quite some work to figure out which factors
51 affect microbial growth in sourdough. Iıve done some work in vitro (which
52 is about to be published: Gänzle et al., Modeling of growth of
53 Lactobacillus sanfranciscensis and Candida milleri in response to process
54 parameters of the sourdough fermentation, Applied and Environmental
55 Microbiology, July 1998); and a colleague of mine, Markus Brandt, has
56 tried to figure out how my "model predictions³ work out during the actual
57 dough fermentation. Taken together, one can state the following:
58 A) The optimum temperature for sourdough lactobacilli is 32 - 33°C. At
59 37°C and 20°C, the generation time is twice as long.
60 B) At 39 and 15°C, the generation time is four times as long.
61 C) At 41°C and 4°C, no growth is observed.
62 For the yeasts, the figures are as follows:
64 B) 32/20 (double generation time)
65 C) 34/14 (fourfold generation time)
67 So: if several refreshments are done above 32°C, the yeasts will drop out
68 eventually. The optimum pH for lactobacilli is 5.0 - 5.5 (which is the
69 initial pH of a sourdough with 5 - 20% inoculum), the minimum pH for
70 growth is 3.8 (they usually produce acid until pH 3.6 is reached).
71 Lactic or acetic concentrations donıt affect growth of lactobacilli very
72 much: this is the reason why the buffering capacity of the flour is so
73 important for the organism (a high buffering capacity in high ash flours
74 means that the lactobacilli produce much acid until the critical pH is
75 reached). It also means, that in doughs that are continuously operated
76 with a high inoculum (more than about 30%), youıll find more yeasts and
77 fewer lactobacilli. Eventually, the lactobacilli flora may change, with
78 more acid tolerant lactobacilli (e.g. L. pontis) prevailing. Such a
79 sourdough is found in the Vollmar and Meuser continuous sourdough
80 fermentation machines (there are 6 operating in Germany, and a diploma
81 candidate in our department characterised the microflora of several of
82 these: as the machine is operated with a 50% inoculum, the pH is never
83 above 4.1 - 4.3, and no L. sanfranciscensis is found in those doughs).
84 Yeasts are different: they donıt mind the pH at all, but are strongly
85 inhibited by acetic acid, and to a much lesser extend by lactic acid.
86 Increasing salt concentrations inhibit growth of lactobacilli, but yeasts
87 tolerate more salt. No salt is added to the sourdough until the final
88 bread dough, but the dough yield affects the salt concentration: with a
89 low dough yield (little water), the salt (ash) is dissolved in a smaller
90 water volume, and the salt concentration goes up: resulting in a slower
92 So much for the "in vitro³ theory. Surprisingly, Markus has found most of
93 the predictions to come true when he was looking at the cell counts at
94 different temperature, size of inoculum, salt concentration, and pH in rye
95 dough. The variation of the inoculum size was interesting: If he reduced
96 the inoculum size by 2, he had to wait almost exactly one generation time
97 (one doubling time of the lactobacilli) longer until the dough has reached
98 the same cell counts, pH, titrable acidity, and so on as the dough with
99 the higher inoculum. This was true for inoculum sizes between 1% and 20%:
100 at 50% inoculum, the pH is so low that the lactobacilli donıt really grow
101 well, and at an inoculum size of 0.1%, the pH and/or the oxygen pressure
102 in the dough are so high that the cells have a lag-time (see above) of an
103 hour. Thus, a scanty inoculum means one generation time longer
105 The generation time of L. sanfranciscensis in rye dough at 28°C is a
106 little less than an hour (figures may vary with different strains in
107 different flours, but itıs not much more or less than that), so if the
108 inoculation size is reduced from 20 to 2.5%, itıll take about three hours
109 more until the dough is ripe.
110 The question is, whether these findings are true for all flours and for
111 all organisms. The strain isolated by Kline and Sugihara does not differ
112 very much from the two strains Iıve been looking at. All the literature
113 available tells me that - as long as weıre looking at sourdoughs with a
114 tradition of continuous propagation - the system behaves the same way.
115 Differences may be between rye flour and white wheat flour: in white wheat
116 flour, the enzyme activities are so low that the organisms may run out of
117 food before the critical pH (lactobacilli) or the critical acetic acid
118 concentration (yeasts) is reached.
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120 This discussion continues in the next post-- DCW
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126 ======================================================
127 From: wagons@connriver.net (Daniel Wing)
128 Subject: Long Technical Post 2
130 Message-ID: <wagons-0301041021200001@port-1-26.wellsriver.connriver.net>
131 Organization: Cookeville Garage
132 Newsgroups: rec.food.sourdough
135 Rye is second to wheat as a bread grain
137 Comment No2: If discussing rye, it may be of importance, that rye quality
138 depends heavily on the weather conditions during the harvest: if is is
139 very humid before and during the harvest, sprouting starts, leading to
140 increased amylase activity. In a dry year, the amylase activities may be
141 rather low, so that the problem with the acidification is not very
142 prominent. It may also be noted that rye not only has a higher amylase
143 activity,a but also a higher protease activity, which is important for the
145 ---------------------------------------------------------
146 In all, about 72 percent of the original kernel is left in most of the
147 white flour produced in the United States.
149 In Germany, the most common bread flour is wheat type 1050 (1.050 g ash
150 per kg) or rye type 1180. Many breads are "Vollkornbrot³. Type 550 (or 55)
151 is used only for white wheat bread, not a very big share in the market.
152 -----------------------------------------------------
153 Rye flour is commercially ground to a range of colors and particle sizes,
154 and the nomenclature is confusing.
156 If very coarsely groung flour is used, it should be swollen in water
157 before the dough mixing, Otherwise, it will take up water during dough
158 fermentation and proofing, and result in too stiff doughs. This is called
159 "Quellstueck³ by German bakers. As far as the enzyme activities go, see
160 comment No2 above. The difference in enzyme activities is also important
161 for the microorganisms: in rye flour they always have enough sugar
162 available due to the high enzyme activities, whereas in white wheat
163 flours, glucose (but not maltose) may be depleted during the fermentation.
164 ----------------------------------------------------------------
165 Rye flour contains a great deal of amylase. Rye amylase resists
166 inactivation by heat to a greater extent than wheat amylase. It is so
167 resistant to inactivation that it is still active when the gelatinization
168 temperature of rye starch is reached in the oven
170 This is a very nice explanation. Also: see above (Comment No2)
171 ----------------------------------------------------------
172 No laboratory test assesses taste, even though there are real differences
173 in the taste and texture of bread baked from otherwise similar flours.
175 This would be impossible, since the flour has no flavor whatsoever. Iıve
176 been preparing a research proposal recently with Markus Brandt and Prof.
177 Hammes in our lab, and Prof. Schieberle, probably the best expert in
178 flavor chemistry of bread, so Iıll go into some detail (and refer to it as
179 comment No3 later on). It may be useful to distinguish between taste and
180 aroma. Taste happens on the tongue, where only salty, bitter, sweet and
181 sour can be evaluated. Aroma is percieved in the nose: during chewing, the
182 volatile compounds diffuse to the receptors (mind that acetic acid, but
183 not lactic acid is volatile. Thus, the latter is just sour, while acetic
184 acid has aroma). There are about 15 compounds each (about 10 of them are
185 the same for wheat and rye bread, furthermore, crust and crumb have
186 different aroma volatiles) with which the impression of rye or wheat bread
187 is given (This is work of Prof. Schieberle in Munich).
188 To group the compounds according to their generation in dough, one may say
190 i), they are produced by fatty acid oxidation by cereal enzymes upon dough
191 mixing (several baking aids contain soy flour with additional lipoxygenase
192 activity, and prolonged storage of whole flour leads to rancidity as
193 well). These compounds have a "green³, "bitter³ "tallowy³ or "metallic³
194 taste - not very pleasant. Lactic acid bacteria and yeasts do inactivate
195 these compounds in part, thus, fermentation reduced the "rancidity³ of the
197 ii) aroma compounds are produced by yeasts and lactobacilli. More of them
198 by yeasts, probably, though acetic acid also plays an important role.
199 These compounds often give a "flowery³, "yeasty³ or "malty³ flavor.
200 iii) The Maillard reaction is extremely important, especially for the
201 crust aroma compounds. However, the precursor chemicals for this type of
202 reactions are amino acids, and the levels of amino acids in flour is verym
203 low. In wheat, there is little, if any proteolytic activity (proteases
204 degrade protein to amino acids), so, whatever amino acids there are
205 produced by enzymes of lactic acid bacteria (there has been nice work done
206 on proteolysis in wheat dough by Dr. Marco Gobbetti at the University of
207 Perugia). In rye, the proteolytic activity of the flour is much higher,
208 but the proteases need acidification to a pH below 5 to have their optimum
209 activity (and, of course, a long fermentation time gives the enzymes more
210 time to work). Sourdough yeasts are consuming amino acids, meaning a
211 sourdough with a high yeast count has fewer amino acids than a dough
212 containing only lactobacilli. Addition of excess amounts of bakerıs yeast
213 (>4%) also leads to an increase of Maillard compounds, but that may not be
214 the aroma a sourdough baker is looking for. The most important flavor
215 compound in rye crust, methional, as well as in wheat crust,
216 2-acetyl-pyrroline, are Maillard products of the amino acids methionine
217 and ornithine, respectively.
218 As I mentionned, weıve been preparing a research proposal to figure out
219 which of the aroma compounds or aroma precursors (meaning chemicals
220 converted to aroma compounds during baking) are formed by which
221 microorganisms. In other words, other than acetic acid production, we
222 donıt know whether or not aroma is produced by yeasts and lactobacilli of
223 sourdough. There are a few good working hypotheses: Some, but not all
224 strains of L. sanfranciscensis convert arginine to ornithine (MOST
225 important flavor precursos in wheat), so this metabolic activity may be of
226 importance. Several other compounds are produced by yeasts (but we donıt
227 know whether the sourdough yeasts are more active than bakerıs yeast), and
228 all L. sanfranciscensis does convert the fatty acid oxidation products to
229 chemicals with less or no aroma intensity - but how this activity compares
230 to straight, bakerıs yeast dough, we donıt know.
231 ============================================
232 continued in next post-- DCW
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239 ======================================================
242 From: wagons@connriver.net (Daniel Wing)
243 Subject: Long lTechnical post 3
245 Message-ID: <wagons-0301041021590001@port-1-26.wellsriver.connriver.net>
246 Organization: Cookeville Garage
247 Newsgroups: rec.food.sourdough
251 Amylase digestion of this damaged starch provides sugar for fermentation
252 and produces dextrins, a class of polysaccharide that is quite
255 See comment No2: lactobacilli and yeast rely on the amylase of the grain
256 as they donıt have starch degrading enzymes. A Spanish group has looked
257 for the development of maltodextrins during sourdough fermentation: as
258 lactobacilli and yeasts donıt like the oligosaccharides, they accumulate
259 during fermentation. The Spanish (C. Collar and M. Martinez-Anaya in
260 Valencia, Spain) think that maltodextrins may delay bread staling, though.
261 ----------------------------------------------------
262 because that enzyme (PHYTASE) is most active in dough between pH 4.3 and
263 4.6, prolonged fermentation with mixed cultures (an acid medium) will
265 It is true that the enzyme is most active IN DOUGH between pH 4.3 and 5,
266 however, the reason is not optimum enzyme activity at this pH, but the
267 fact that CaMg-Phytate is insoluble and thus not available for enzymatic
268 cleavage at a higher pH. (The first work during my diploma thesis was to
269 look for phytase enzymes in lactobacilli from sourdough. After 8 weeks, I
270 figured out that there is none, and shortly thereafter it became clear
271 that both wheat and rye have sufficient phytase activity, all it takes is
273 -----------------------------------------------------
274 I chose to write "natural leaven" because it is less awkward than "mixed
275 ferment cultured from the environment and sustained with repeated
278 "Sustained with repeated inoculation³ is better than anything I was
279 writing to say the same thing. Cultured from the environment³ is certainly
280 true - L. sanfranciscensis and the yeasts must come from somewhere - but
281 somewhat misleading, as these organisms most probably do not originate
282 from the grain, or the flour (Marco Gobbetti, whom I mentionned earlier
283 has been looking for L. sanfranciscensis on all kinds of Italian wheat
284 flours, and he has not found any. In every Italian dough "sustained with
285 repeated inoculation³ youıll find L. sanfranciscensis to be the dominating
286 species, though. No other scientist has been able to isolate L.
287 sanfranciscensis from any other source than sourdough, but all sourdough
288 "sustained etc.³ Contain this organism as the dominating flora. A possible
289 source may be the humans: there are all kinds of lactobacilli thriving in
290 the mouth, the intestines, etc. Hammes met a South African Microbiologist
291 who claimed to have isolated L. sanfranciscensis from the teeth of
292 pre-school children. The data is not published, so I donıt know what
293 science is behind this claim. But, whereever L. sanfranciscensis comes
294 from, it most probably does not come from the flour. (Thats comment No4)
295 --------------------------------------------------------
296 Natural leavens are not all the same. Not only are there many strains of
297 yeast and bacteria that can form them, we need terms in English for the
298 various stages of natural leavens.
300 One may think of all the "sourdough stages³ as just a piece in a infinite
301 chain of repeated inoculations. Some sourdoughs are quite close to
302 infinity, as far as the generations go. You certainly know Carl Griffith
303 sourdough (claimed to have survived since the days of the Oregon Trail);
304 the dough weıve been working with, Böcker Reinzucht Sauer, a rye starter
305 that thas the reputation of being one of the best rye starters available
306 (Spicher says so, we do, and the Spanish group has been working with it as
307 well), is well above 50 yeast "old³. Then, the definition of e.g. "three
308 stage sourdough processes³ does make no sense. What makes is fascinating
309 is that the microbiology of Böcker Reinzuch Sauer HAS NOT CHANGED in the
310 past 30 yeast, i.e. since people started to do microbiology with the
311 dough. There are two strains of L. sanfranciscensis, and one yeast, C.
312 milleri. The "modeling³ I mentioned in comment No1 was done with these
313 three organisms. Remarkably, the two strains of L. sanfranciscensis
314 reacted almost identically on changes of pH, temperature, etc. Then, the
315 definition of e.g. "three stage sourdough processes³ does make no sense.
316 -----------------------------------------------------
317 This selection leaves it (COMMERCIAL YEAST) specialized for a narrow range
318 of fermentation characteristics that favor rapid gas production over
319 flavor production or other possibly desirable qualities (resistance to
320 bread spoilage, for instance).
322 This could be also said for sourdough lactobacilli and yeasts: As the
323 dough is continuously refreshed, those strains are selected that grow
324 fastest in dough. This is probably a much more harsh and effective
325 selection than what is done for the bakerıs yeast. Fortunately, what is
326 good for the sourdough lactobacilli seems also to be good for bread
327 quality (There are other microorganis in fermented food that require the
328 man-made habitat: e.g. Tetratenococcus halophilus growing only in soy
329 mashes, and Oenococcus oeni, occuring in wine only.) What is important, is
330 that as soon as you change your parameters, you may change the microflora.
331 E.g., if the dough is fermented at 33 instead of 28°C, yeasts will drop
332 out, and above 37 - 38°C, the flora will change altogether, with
333 thermophilic lactobacilli dominating. See comment No1.
334 ---------------------------------------------------------
335 The yeast and bacteria in natural leavens are considered native or wild
336 because the cultures are started with organisms recovered from
339 The fermentation starts with flour microorganisms, but - see comment No4 -
340 the sourdough lactobacilli and yeasts do probably not originate from the
341 grain. And later: the organisms have been refined by thousands and
342 thousands of sourdough - refreshments, much more effective than any
343 microbiologist of food scientist could ever be. (Besides, we know what
344 kind of organisms do grow in sourdough - but how flavor production takes
345 place, and which fermentation products delay bread staling is largely
346 unknownm - so other than gas production, I could not think of a property
347 of lactobacilli in which to select a strain. And gas production, as youıve
348 rightfully pointed out, is certainly not the right criterium.)
349 ----------------------------------------------------------
350 The conditions under which a culture is developed and then maintained can
351 select out strains of yeast and bacteria that have special
352 characteristics, and the typical yeasts present in the air and soil in
353 different locations also vary somewhat in their properties and their
354 interactions with lactobacilli. This kind of co-evolution makes some
355 natural leavens remarkably stable when regularly maintained. The more
356 regular and consistent the maintenance, the more predictable the rising
357 power, microbiological composition, acid balance (acetic/lactic) and acid
360 This is important (although I donıt think that the yeasts from air and
361 soil do matter). But the consistency in maintenance is crucial (one is
362 allowed to err to one side or the other from time to time, though).
363 -------------------------------------------------------------------
364 ============================================
365 continued in next post-- DCW
371 ======================================================
373 ======================================================
374 From: wagons@connriver.net (Daniel Wing)
375 Subject: Long Technical Post 4
377 Message-ID: <wagons-0301041022540001@port-1-26.wellsriver.connriver.net>
378 Organization: Cookeville Garage
379 Newsgroups: rec.food.sourdough
383 Since many people new to natural leavens would like to bake San Francisco
384 sourdough, Desem bread, or German rye bread, let's look at some of their
385 characteristics, as determined by their leavens, ingredients, and
388 The microflora of German rye sour and Sanfrancisco sourdough is (almost)
389 identical. The difference is raw material and production process. Prof.
390 Hammes thinks that L. sanfranciscensis isolated from wheat or rye may have
391 different properties (e.g. degradation of arginine to ornithine, see
392 comment No3, or proteolytic activity (see comment No2: wheat has less
393 proteolytic activity by itself than rye). He still has to prove his point,
395 -----------------------------------------------------------
396 That yeast is also resistant to a natural antibiotic made by the bacteria.
398 The most "antibiotic³ compound in sourdough is acetic acid. Although I
399 mentionned earlier that Candida milleri from Böcker Reinzucht Sauer (The
400 Saccharomyces exiguus described by Kline and Sugihara has been renamed to
401 Candida milleri as well) is more sensitive to acetic acid than the
402 lactobacilli, it certainly is much more resistant than bakerıs yeast.
403 Gobbetti says that L. sanfrancisco produces other organic acids that may
404 inhibit yeast growth, but I donıt know wheter or not the concentration in
405 the dough is high enough to make a difference. As far as I know, no other
406 antimicrobial compound in dough has been characterised.
407 -----------------------------------------------------------
408 Most German rye bread has at least 30 percent rye
410 I have the figures: 60% is "mixed rye bread³ containing both rye and
411 wheat, but more of the former. As far as the bread goes, rye only about as
412 important as wheat only. The situation is different for bagels, pretzels,
413 and so on. There is increasing interest in wheat sourdoughs: the 1 - 5%
414 addition of sourdough, which is sometimes replaced by a dried and "dead³
415 sourdough works, but not quite as well as it could. Which is why industry
416 is funding flavor research at the Universities of Hohenheim and Munich...
417 ----------------------------------------------------------
418 Vollmar and Meuser showed that the rate of bacterial reproduction after
419 inoculation is self-regulated, within limits: if you add a small inoculum,
420 the bacteria will multiply faster than they will if it is larger, so the
421 static population (say 1,650 million cells/cc) is reached at the same time
422 in either case, about three and one-half hours.
424 The Vollmar and Meuser sourdough machine is not a very good example: as
425 pointed out in comment No1, it operates with an inoculum of 50%, which
426 makes the dough so acid from the beginning on the the lactobacilli donıt
427 like to grow fast. Between 1 and 20% inoculum, lactobacilli grow at the
428 same speed (giving rise to the dependency of fermentation time and
429 inoculum size explained earlier). The Vollmar and Meuser machine also has
430 a rather high yeast content (if youıve read their publication in Cereal
431 Chemistry; yeasts are above 100 million or more than 10% or the total cell
432 counts, while "normal³ starters such as the Sanfrancisco starter of the
433 Böcker Reinzucht Stater have only around 10 million or about 1% of the
435 --------------------------------------------------------
436 When cultures are fermented at higher temperatures, non-pathogenic
437 acid-tolerant contaminants such as Pediococcus (makes too much lactic
438 acid) and Acetobacter (makes to much acetic acid) can intrude and
439 dominate, affecting taste.
441 Pediococcus is probably less acid tolerant than L. sanfranciscensis, but
442 it grows at higher temperatures (as mentionned above, sanfranciscensis
443 does not like more than 35 - 37°C. Acetobacter is of no importance in
444 sourdoughs: it strictly requires oxygen for growth, and sourdough becomes
445 anaerobic (=without oxygen) very quickly due to the metabolism of yeasts
446 and lactobacilli. If youıve ever seen a vinegar fermenter you will notice
447 that several hundred liter of air are pumped through a liter of vinegar
448 during an hour: it is almost impossible to aerate sourdough in such a way.
449 --------------------------------------------------------------
450 Dr. Sugihara, who participated in the characterization of the flora of San
451 Francisco sourdough and several other cultures, was asked whether natural
452 sourdough cultures could be contaminated with commercial yeast. His reply
453 was no, not if you have a stable culture that is continuously maintained
454 with the same conditions and ingredients.
456 Dr. Sugihara is certainly right here. There was an experiment done by a
457 Dutch group: bakerıs yeast didnıt survive more than two refreshments. I
458 think that itıs the acetate that kills the yeast as its less acetate
459 tolerant than sourdough yeasts.
460 And to the margin note right next (CONCERNING THE ABILITY OF BACTERIAL
461 FERMENTATION TO RAISE A LOAF OF BREAD, WITHOUT YEAST): Weıve done the
462 experiments, it works quite well without yeast. The volume is somewhat
463 smaller, though. Markus Brandt has estimated the contribution of yeasts
464 and lactobacilli to gas production in a "normal³ sourdough: about 50%
465 comes from lactobacilli and yeasts each. The yeasts are fewer in numbers,
467 --------------------------------------------------------
468 Bakers are interested in the acids produced by leaven microbes because
469 much of the distinctive flavor produced by leaven microbes comes in the
470 form of organic acids that are products of fermentation.
472 The production of lactic acid in dough in determined mainly by the
473 buffering capacity of the flour, i.e. the ash content. Dough yield and
474 temperature are much less important; as far as Spichers investigations go,
475 I think that the higher lactic acid concent of doughs with higher
476 temperatures or higher dough yields he measured is due mainly to the
477 faster fermentation at these conditions. (this holds true if you calculate
478 the lactate produced on the amount of flour in the dough: this ratio is
479 fairly constant). The amount of acetic acid produced is controlled mainly
480 on the availability of fructose. L. sanfranciscensis produced lactic acid
481 and ethano (and carbon dioxide) from maltose or glucose. If the organism
482 wants to produce the more oxidized end product, acetic acid, another
483 substrate must be reduced. L. sanfranciscensis reduced 2 moles of fructose
484 to mannitol per mole of acetic acid formed. The ratio of mannitol to
485 acetic acid in dough os about 1.8, fairly close to the theoretical value
486 of 2 if fructose was the only co-substrate that is reduced. During
487 fermentation, L. sanfrancisco starts to produce lactic acid and acetic
488 acid first, and forms lactic acid and ethanol only if the fructose is
489 depleted. There is a lot of fructose in dough, but not all of it is
490 available for the lactobacilli. Yeasts liberate some of the fructose bound
491 in glucofructans that thus becomes available for the lactobacilli (there
492 is some nice work that has been done by the Sugihara group, Saunders et
493 al., cereal chemistry, 1972 or 1973). If you to too high with the
494 temperature, you slow down yeast growth, and the acetic acid levels in the
495 dough decrease. For bakers, an easy way to increase the acetic acid
496 content is to add sugar 8that is sucrose,a consisting of glucose and
497 fructose). This wonıt increase the total titrable acidity, though, as that
498 is determined by the buffering capacity. Sugar addition (not too much, 1
499 or 2%) may speed up fermentation in white wheat flours: as mentionned
500 above, in contrast to whole wheat flour and rye flours, the enzyme
501 activities and thus the sugar concentrations are rather low and may limit
503 As far as the influence of acetic acid and lactic acid on flavor go:
504 lactic acid has no influence on aroma, only on taste, while acetic acid is
505 an aroma volatile. So, I think it is not so much the ratio of lactic to
506 acetic acid, but more simply the acetic acid content that matters.
507 ------------------------------------------------------------
508 Natural leavens should be actively fermenting and reproducing when they
509 are incorporated into a dough
511 Yeasts in dough donıt have to rely on oxygen for growth: if that were the
512 case, they woudnı t be there.
513 ----------------------------------------------------------------------
514 The more accepted and consistently successful way to store a culture for a
515 month or so is to make a fresh and very stiff storage leaven, put it in a
518 Such leavens may keep up to almost three month (my sister had a baby in
519 March and didnıt use her starter for almost three month. It was stored the
520 way you described here, and did come out well upon refreshment. The Böcker
521 Reinzuchtsauer is also distributed as stiff, refrigerated product. I think
522 the company does not guarantee storage stability of more than 4 weeks,
524 ----------------------------------------------------------------------
525 Still there may be someone out there who does need to start a leaven
526 because of some terrible misfortune--
528 I think it does not matter when the first batch of a new sourdough stinks
529 - the good bacilli will come out eventually, and they may come faster if
530 fermentation is done around 25 - 30°C (as mentionned earlier, the
531 temperature optimum of L. sanfranciscensis is 32 - 33°C). There has been
532 nice work done in Rudi Vogels lab on the microflora of a freshly started
533 sourdough: first, there are Enterobacteria (Escherichia coli, Salmonella,
534 Enterobacter), highly undesirable organism that stink terribly, then there
535 are homofermentative lactobacilli (good, but no gas production), then
536 acid-tolerant, heterofermentative lactobacilli. I think, this took about
537 48 hours at 30°C. The stink at the beginning does not matter as the
538 organisms will be diluted out or die eventually. No L. sanfranciscensis,
539 though, these will occur only after repeated refreshments. Peter Stolz of
540 the Böcker company told me that it takes about two weeks of repeated
541 inoculations to get a good "sanfranciscensis³ sourdough. I donıt know
542 whether or not this process was sped up in his case as, due to his
543 workplace, his skin is all covered with L. sanfranciscensis.
544 -----------------------------------------------------------------
545 My biggest disagreement with her, though (NANCY SILVERTON), is about the
546 amount of material one should use in a starter.
548 I agree with you: one g of dough is one billion lactobacilli and 10
549 million yeasts: more than enough. In the lab, Iım doing most experiments
550 on a 1/10 ml scale, for dough refreshments at home, it does not get much
551 smaller than 10 g: itıs difficult to handle smaller amounts.
552 -------------------------------------------------------------
553 If leaven refreshment intervals are excessive
555 The main criterion of sourdoughs containing L. sanfranciscensis is the
556 repeated, frequent refreshment (not counted the storage in the
557 refrigerator). Peter Stolz said that one every 24 hours will suffice, if
558 intervals are much longer than that (lets say more than 3 days),
559 different, more acid tolerant organisms may evolve (e.g. L. pontis as
560 found in the Vollmar and Meuser Breasd maschines: these are refreshed
561 frequently, but with a very high inoculum).
562 ---------------------------------------------------------------------
563 Refreshment schedules are always dependent on temperature.
565 See my earlier comment on the temperature dependency of growth of L.
566 sanfranciscensis and Candida milleri. Most of the typical sourdough yeasts
567 resemble C. milleri with respect to the temperature sensitivity (i.e. no
569 -------------------------------------------------------------
570 Acidity can be expressed as flavor (an acid flavor), as pH, or as total
573 That a good explanation of the total titrable acidity concept. (I find
574 students almost done with their degree still have difficulties with this
576 -------------------------------------------------------------------
577 At any given temperature the thinner starter will ferment faster and reach
578 a lower pH; but will not contain as much acid.
580 If you calculate the amount of acid produced on the weight of the flour
581 rather than the dough weight, the outcome -lactic acid per g flour -
582 should be pretty independent on dough consistency (not if very stiff
583 doughs are produced: the combined salt and acid stress leads to a
584 decreased acid production). Markus Brandt observed this in doughs (rye
585 flour, TA 180) if more than 2% salt were added.
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587 Together, caramels and Maillard products are responsible for much of the
588 flavor and aroma of fresh yeasted bread, although of these two, Maillard
589 products are moch more intensely aromatic.
591 This is right for both yeasted breads and sourdough breads, however, it is
592 important to note that whatever chemicals are reacting with each other
593 during baking must be formed during dough fermentation. (Schieberle in
594 Munich has done several nice studies: he supplied doughs with amino acids
595 and demonstrated that the levels of aroma compounds in the bread were
596 increased). So, formation of aroma precursors during dough fermentation is
597 crucial for the Maillard reaction.